Fire Behavior of Prestressed Stayed Columns: Critical Temperature and Mode Transition

Abstract

Prestressed stayed columns are vulnerable to the stiffness loss in fire. This study aims to reveal the fire resistance and failure behavior of this system. Based on the theoretical optimum prestress, the fire behavior of prestressed stayed columns is investigated using transient state analysis within ABAQUS version 6.14.4 with both the uniform and nonuniform temperature distributions considered. Results show that the stayed columns’ approximate failure is above 600°C, and the system usually fails with stay slackening and sometimes with stay retension. If the reflective symmetric buckling mode is dominant and the linear buckling loads of reflective and rotational symmetric modes are numerically close, unstable behavior such as ‘mid-span reverse’ and ‘mode transition’ can be observed in conjunction with stay slackening at the heating stage. For the nonuniform temperature distribution, ‘mode transition’ occurs in most cases, but this transition only reduces the critical temperature significantly in the preceding special cases. Prestress is recommended to be higher than the theoretical optimum prestressing level to avoid premature stay slackening and ‘mode transition’, but for the preceding special cases with nonuniform temperature distribution, raising prestressing levels may reduce the critical temperature owing to the different failure modes from obvious ‘mode transition’. This study would provide basis to establish the design guidance for stayed columns in fire in the future. Prestressed stayed columns are vulnerable to fire due to material weakening and instability. This study aims to investigate the failure temperature, and reveal the failure mechanism of this system in fire. Results show that the stayed columns approximate failure was above 600°C, and the system usually fails with stay slackening and complicated deflection. For the stayed columns with specific buckling behavior, the deformed shape at the heating stage is unstable, and the deflection direction and deformation features may change accidentally. This behavior reduces the fire resistance of this system and leads to accidental large deformation. This study can provide a basis to establish the design guidance for stayed columns in fire, and give suggestions for the response prediction and collapse warning for the stayed columns exposed to fire.